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Solid-to-molecular-orientational-hexatic melting induced by local environment determined defect proliferations

Chinese physics B 2022年第12期31卷 396-403页

作者： Zhanglin Hou Jieli Wang Ying Zeng Zhiyuan Zhao Xing Huang Kun Zhao Fangfu Ye Wenzhou Institute University of Chinese Academy of SciencesWenzhou 325001China Key Laboratory of Systems Bioengineering(Ministry of Education) School of Chemical Engineering and TechnologyTianjin UniversityTianjin 300072China School of Physical Science University of Chinese Academy of SciencesBeijing 100049China Research Center of Computational Physics School of Mathematics and PhysicsMianyang Teachers’CollegeMianyang 621000China Sichuan Provincial People’s Hospital University of Electronic Science and Technology of ChinaChengdu 610054China Institute of Fundamental and Frontier Sciences University of Electronic Science and Technology of ChinaChengdu 610054China Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China Songshan Lake Materials Laboratory Dongguan 523808China Oujiang Laboratory(Zhejiang Laboratory for Regenerative Medicine Vision and Brain Health)Wenzhou 325001China

Two-dimensional(2D)melting is a fundamental research topic in condensed matter physics,which can also provide guidance on fabricating new functional ***,our understanding of 2D melting is still far from being complete due to existence of possible complicate transition mechanisms and absence of effective analysis ***,using Monte Carlo simulations,we investigate 2D melting of 60°rhombs which melt from two different surface-fullycoverable crystals,a complex hexagonal crystal(cHX)whose primitive cell contains three rhombs,and a simple rhombic crystal(RB)whose primitive cell contains one *** melting of both crystals shows a sequence of solid,hexatic in molecular orientation(Hmo),and isotropic phases which obey the Berezinskii-Kosterlitz-Thouless-Halperin-Nelson-Young(BKTHNY)***,local polymorphic configuration(LPC)based analysis reveals different melting mechanisms:the cHX-Hmotransition is driven by the proliferation of point-like defects during which defect-associated LPCs are generated sequentially,whereas the RB-Hmotransition is driven by line defects where defect-associated LPCs are generated *** differences result in the observed different solid-Hmotransition points which areφA=0.812 for the cHX-HmoandφA=0.828 for the *** work will shed light on the initial-crystal-dependence of 2D melting behavior.

关键词： two-dimensional melting phase transition molecular-orientational forming liquid crystal local environment melting mechanism

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Interface Width Effect on the Weakly Nonlinear Rayleigh–Taylor Instability in Spherical Geometry

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Chinese physics Letters 2020年第7期37卷 43-46页

作者： Yun-Peng Yang Jing Zhang Zhi-Yuan Li Li-Feng Wang Jun-Feng Wu Wun-Hua Ye Xian-Tu He School of Physics Peking UniversityBeijing 100871China Center for Applied Physics and Technology HEDPSand College of EngineeringPeking UniversityBeijing 100871China Institute of Applied Physics and Computational Mathematics Beijing 100094China

Interface width effect on the spherical Rayleigh–Taylor instability in the weakly nonlinear regime is studied by numerical *** Legendre perturbation mode Pn with wave number Kn and interface half-width L,the commonly adopted empirical linear growth rate formulaγnem(L)=γn/√1+KnL is found to be sufficient in spherical *** the weakly nonlinear stage,the interface width affects the mode coupling *** development of the mode P2n is substantially influenced by the interface ***,the nonlinear saturation amplitude increases with the interface width.

关键词： interface nonlinear weakly

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ViSymRe: Vision-guided Multimodal Symbolic Regression

arXiv

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arXiv 2024年

作者： Li, Da Yin, Junping Xu, Jin Li, Xinxin Zhang, Juan Academy for Advanced Interdisciplinary Studies Northeast Normal University Jilin Changchun130024 China Institute of Artificial Intelligence Beihang University Beijing100191 China Institute of Applied Physics and Computational Mathematics Beijing100094 China National Key Laboratory of Computational Physics Beijing Beijing100088 China School of Mathematical Sciences East China Normal University Shanghai200241 China Shanghai Zhangjiang Institute of Mathematics Shanghai201203 China

Symbolic regression automatically searches for mathematical equations to reveal underlying mechanisms within datasets, offering enhanced interpretability compared to black box models. Traditionally, symbolic regression has been considered to be purely numeric-driven, with insufficient attention given to the potential contributions of visual information in augmenting this process. When dealing with high-dimensional and complex datasets, existing symbolic regression models are often inefficient and tend to generate overly complex equations, making subsequent mechanism analysis complicated. In this paper, we propose the vision-guided multimodal symbolic regression model, called ViSymRe, that systematically explores how visual information can improve various metrics of symbolic regression. Compared to traditional models, our proposed model has the following innovations: (1) It integrates three modalities: vision, symbol and numeric to enhance symbolic regression, enabling the model to benefit from the strengths of each modality;(2) It establishes a meta-learning framework that can learn from historical experiences to efficiently solve new symbolic regression problems;(3) It emphasizes the simplicity and structural rationality of the equations rather than merely numerical fitting. Extensive experiments show that our proposed model exhibits strong generalization capability and noise resistance. The equations it generates outperform state-of-the-art numeric-only baselines in terms of fitting effect, simplicity and structural accuracy, thus being able to facilitate accurate mechanism analysis and the development of theoretical models. Copyright © 2024, The Authors. All rights reserved.

关键词： Equations of state

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Determination of the Landé gJ factor and Zeeman coefficients in ground-state 171Yb+ and their applications to quantum frequency standards

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Physical Review A 2025年第1期111卷 012814-012814页

作者： Jize Han Benquan Lu Yanmei Yu Jiguang Li Zhiguo Huang Jingwei Wen Ling Qian Lijun Wang State Key Laboratory of Precision Measurement Technology and Instruments Department of Precision Instrument Tsinghua University Beijing 100084 China China Mobile (Suzhou) Software Technology Company Limited Suzhou 215163 China National Time Service Center Chinese Academy of Sciences Xi'an 710600 China Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China University of Chinese Academy of Sciences Beijing 100049 China Institute of Applied Physics and Computational Mathematics Beijing 100088 China Department of Physics Tsinghua University Beijing 100084 China

We report the determination of the Landé gJ factor and Zeeman coefficients for the ground-state of 171Yb+, relevant to microwave quantum frequency standards (QFSs). The gJ factor is obtained by using two independent methods, the multiconfiguration Dirac-Hartree-Fock and multireference configuration-interaction methods, yielding a consistent value of 2.002615(70). The first- and second-order Zeeman coefficients are determined as 14010.78(49)Hz/µT and 31.0869(22)mHz/µT2, respectively, based on the calculated gJ factor. These coefficients enable reduced magnetic-field-induced uncertainties, improving the accuracy of the 171Yb+ microwave QFSs. The results reported in this work also offer potential for improved constraints on variations in fundamental constants through frequency comparisons and advancing trapped-ion quantum computers based on the ground-state hyperfine splitting of 171Yb+.

关键词： Trapped ions

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Feasibility of extracting the proton weak charge from quantum-control measurements of atomic parity violation on the 2s−3s or 2s−4s transition in hydrogen

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Physical Review A 2024年第1期109卷 012808-012808页

作者： Jiguang Li (李冀光) Andrei Derevianko D. S. Elliott Institute of Applied Physics and Computational Mathematics Beijing 100088 China Department of Physics University of Nevada Reno Nevada 89557 USA Department of Physics and Astronomy Purdue University West Lafayette Indiana 47907 USA School of Electrical and Computer Engineering Purdue University West Lafayette Indiana 47907 USA Purdue Quantum Science and Engineering Institute Purdue University West Lafayette Indiana 47907 USA

We explore the feasibility of extracting electroweak observables from a measurement of atomic parity violation in hydrogen. Our proposed quantum-control scheme focuses on the 2s−3s or 2s−4s transitions in hydrogen. This work is motivated by the recently observed anomaly in the W-boson mass, which may substantially modify the Standard Model value of the proton weak charge. We also study the accuracy of the previously employed approximations in computing parity-violating effects in hydrogen.

关键词： Atomic & molecular structure Coherent control W & Z bosons

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Tensor Nonconvex Unified Prior for Tensor Recovery

SSRN

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SSRN 2024年

作者： Yin, Junping Sun, Jianing Wu, Yumo School of Mathematics and Statistics Northeast Normal University Changchun130024 China Northeast Normal University Changchun130024 China Institute of Applied Physics and Computational Mathematics Beijing100094 China Shanghai Zhangjiang Institute of Mathematics Shanghai201203 China

Tensor data, such as hyper-spectral images and multi-frame videos, have gained significant attention in practical applications. However, the inherent degradation phenomena during data acquisition, including noise and missing pixels, give rise to a series of ill-posed inverse problems that need to be addressed. Currently, the rational exploration of prior knowledge for tensor recovery, including global low-rankness and local smoothness, has emerged as a common concern. Inspired by recent notable works, this paper proposes a novel tensor non-convex unified prior term, which employs weighted tensor Schatten p-norm as a rank surrogate function in the gradient domain. The new prior can yield a regularizer that effectively captures low-rankness and smoothness and is applied to tensor completion and tensor robust principal component analysis models. An efficient algorithm is developed by using the alternating direction method of multipliers and its convergence analysis is also provided. Extensive experimental results demonstrate that the proposed method outperforms the state-of-the-art methods, particularly in cases of high missing rates and strong noise levels. © 2024, The Authors. All rights reserved.

关键词： Tensors

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Pre-training strategy for solving evolution equations based on physics-informed neural networks

arXiv

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arXiv 2022年

作者： Guo, Jiawei Yao, Yanzhong Wang, Han Gu, Tongxiang Graduate School of China Academy of Engineering Physics Beijing100088 China Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Beijing100088 China HEDPS CAPT College of Engineering Peking University Beijing China

The physics informed neural network (PINN) is a promising method for solving time-evolution partial differential equations (PDEs). However, the standard PINN method may fail to solve the PDEs with strongly nonlinear characteristics or those with high-frequency solutions. To address this problem, we propose a novel method named pre-training PINN (PT-PINN) which can improve the convergence and accuracy of the standard PINN method by combining with the resampling strategy and the existing optimizer combination technique. The PT-PINN method transforms the difficult problem on the entire time domain to relatively simple problems defined on small subdomains. The neural network trained on small subdomains provides the neural network initialization and extra supervised learning data for the problems on larger subdomains or on the entire time-domain. By numerical experiments, we demonstrate that the PT-PINN succeeds in solving the evolution PDEs with strong non-linearity and/or high frequency solutions, including the strongly nonlinear heat equation, the Allen-Cahn equation, the convection equation with high-frequency solutions and so on, and that the convergence and accuracy of the PT-PINN is superior to the standard PINN method. The PT-PINN method is a competitive method for solving the time-evolution PDEs. Copyright © 2022, The Authors. All rights reserved.

关键词： Time domain analysis

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High-accuracy detection of three-dimensional free surface for smoothed particle hydrodynamics based on the continuous global volume scanning

High-accuracy detection of three-dimensional free surface fo...

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中国力学大会-2021+1

作者： Wenbin Liu Dongjun Ma Mingyu Zhang An-Min He NanSheng Liu Pei Wang Department of Modern Mechanics University of Science and Technology of China Institute of Applied Physics and Computational Mathematics

1、Introduction Smoothed particle hydrodynamics(SPH) is a representative Lagrangian particle *** the SPH method,the material is discretized into a series of particles with independent *** to its Lagrangian and meshles... 详细信息

关键词： High-accuracy detection of three-dimensional free surface for smoothed particle hydrodynamics based on the continuous global volume scanning

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Finite-temperature phonon dispersion and vibrational dynamics of BaTiO3 from first-principles molecular dynamics

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Physical Review B 2022年第1期105卷 014304-014304页

作者： Xiaohan Zhang Chunyi Zhang Cui Zhang Ping Zhang Wei Kang HEDPS Center for Applied Physics and Technology and School of Physics Peking University Beijing 100871 China HEDPS Center for Applied Physics and Technology and College of Engineering Peking University Beijing 100871 China Institute of Physics Chinese Academy of Sciences Beijing 100190 China Institute of Applied Physics and Computational Mathematics Beijing 100088 China

A systematic investigation of the finite-temperature phonon dispersion, including its smearing and temperature effects, is carried out using autocorrelation function method together with first-principles molecular dynamics method along the [001] direction of BaTiO3, as an illustrating example of entropy-stabilized structures. A unique anharmonicity in the cubic phase mainly derived from the interactions between titanium and oxygen atoms is revealed, which provides extremely strong damping and smearing to longitudinal optical phonons but no discernible effect on the shift of phonon energies. The anharmonicity gives rise to a nearly constant density distribution in a cubic region around the equilibrium position of the relative motion of titanium atoms with respect to oxygen atoms. These results may help to gain a further insight into complex interactions in entropy-stabilized structures and provide an essential benchmark reference to the development of the promising machine-learning based molecular dynamics methods for the investigation of phonon properties.

关键词： Acoustic phonons Optical phonons Paraelectrics Single crystal materials Density functional theory Molecular dynamics

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Layer Hall counterflow as a model probe of magic-angle twisted bilayer graphene

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Physical Review B 2024年第15期109卷 155114-155114页

作者： Jihang Zhu Dawei Zhai Cong Xiao Wang Yao Condensed Matter Theory Center and Joint Quantum Institute Department of Physics University of Maryland College Park Maryland 20742 USA Max Planck Institute for the Physics of Complex Systems 01187 Dresden Germany New Cornerstone Science Laboratory Department of Physics the University of Hong Kong Hong Kong China HKU-UCAS Joint Institute of Theoretical and Computational Physics at Hong Kong Hong Kong China Institute of Applied Physics and Materials Engineering University of Macau Taipa Macau SAR China

The recent constructions of flat moiré minibands in specifically twisted multilayer graphene and twisted transition metal dichalcogenides (TMDs) have facilitated the observation of strong correlations with convenient tunability. These correlations in flat bands result in band dispersion heavily influenced by carrier densities, leading to filling-dependent quasiparticle band renormalizations. Particularly, in magic-angle twisted bilayer graphene (MATBG), the band structure—including the quasiparticle energy and wave function—is crucial in understanding the correlated properties. Previous theoretical studies have demonstrated the presence of a time-reversal-even charge Hall counterflow in response to a direct current (DC) electric field in twisted bilayers as chiral structures. In this study, we show that such layer Hall counterflow can serve as a sensitive probe for MATBG model parameters, which are currently ambiguous as a result of unavoidable structural relaxation and twist-angle disorder. We present the layer Hall counterflow and the associated in-plane magnetization for three different MATBG continuum models, based on which many-body interacting models have been widely applied to study strong correlations in MATBG. At the single-particle level, our findings indicate notable differences in layer-projected Hall conductivity, both in magnitude and sign, between different MATBG continuum models. Furthermore, our self-consistent Hartree calculations, performed on each of these single-particle continuum models, reveal renormalized layer-projected Hall conductivity by the self-consistent Hartree field.

关键词： Electrical conductivity Electronic structure Hall effect Transport phenomena 2-dimensional systems Strongly correlated systems Twisted heterostructures Band structure methods Boltzmann theory k dot p method

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